Visco-elastic foam is sometimes used to form mattresses and other body supports, has the ability to conform to a user's body, and can provide pressure relief for the user's body. Many types of visco-elastic foam have a glass transition temperature at least partially within the range of temperatures at which a room can be or is likely to be maintained (e.g., 10-30° C.). Therefore, for such visco-elastic foams, the temperature of the visco-elastic foam at least partially determines the firmness of the body support. As the temperature of the body support's environment increases (such as by an increase in room temperature and/or by transmission of heat to the body support from a user's body), the firmness of the body support can be reduced. Alternatively, as the temperature of the body support's environment decreases (such as by a decrease in room temperature and/or reduction in the amount of heat provided to the body support by a user), the firmness of the body support can be increased.
A particularly desirable feature for many body supports is the ability to adjust the hardness of the body support. However, the ability to control the firmness of body supports comprising visco-elastic foam has heretofore been limited. Body supports comprising visco-elastic foam having a hardness that can be adjusted by a user would be welcome additions to the art.